Cartridge fuse



May 6, 1930 THIERY ET AL 1,757,753

CARTR IDGE FUSE Filed Sept. 16, 1927 FATE i UFFEG UNITED v STATES FRITZ 'THIEIBY, OF BERLIN-SIEMENSSTADT, AND HERMANN G-OETSCH, OF BERLIN- CHARLOTTENBURQ GERMANY, ASSIGNORS T0 SIEMENS & HALSKE AKTIENGE- SEI LSGHAFT, WERNERWERK, 0F SIEMENSSTADT, NEAR BERLIN, GERMANY CARTRIDGE FUSE Application filed September 16, 1927, Serial No. 220,025, and in Germany November 9, 1926.

I The object of the present invention is a cartridge fuse with one or with a plurality of heat coils which are soldered with an easily melted solder. The invention is particularly adapted for the protection of apparatus operating with low tension, such as the equipment used in telephone and other com- .municating systems.

In the drawing annexed- Fig. 1 is a view of a sectional view of a fuse;

Fi 2 is an enlarged view of the heat coils 1 an 2 of Fig. 1;

Fig. 3 is another form of heat coil em bodying the invention;

Fig. 4 is a View showing a method of soldering shorter turns of constantan wire.

According to the invention, the dimensions of the resistance wire of the heat coils are such that the least possible resistance corresponds to a high relative value of the melting current in ampere and static load capacity in joules. To explain this a little more in detail, it may be pointed out that a distinction must be drawn between steady loading of a fuse, as for instance by continuous current flow, and momentary loading due to transient currents which may be caused by atmospheric discharges or by changes in current in adjacent high tension lines. The effect of these momentary currents can be easily reproduced in the laboratory by the dis charge current of a condenser. Tests have therefore been made by using a condenser which was charged up to a specific Voltage and then discharged through the fuse. The enof a charged condenser is represented by and is measured in joules. It wasfound in practice that fuses'which resist the discharge of a condenser the electrostatic energy of which isascertained to be 12 joules, will withstand almost all atmospheric discharges or discharges of power lines which are likely to occur.

It is desirable that atmospheric discharges, such as take place during stormy weather, shall not blow the fuses, since the equipment is sufficiently protected by the lightning arrester. -Hence, theobject of the invention is to design a fuse which While blowing with ily be so constructed that their melting current is about 0.5 amperes, steady load, wit a static load capacity of about 12 joules and a resistance of about 2 ohms.

It will be apparent that such fuses are of great importance for protecting feeble current apparatus against excess currents due to any cause, particularly those due to the influence of adjacent power lines. The melting current of known fuses is usually so high (about 8 amperes), that the excess tension fuses or small lightning arresters are generally already damaged before the fuses operate. If, however, the tension fuses are placed in series with fuses of low steady melting current and high static load capacity, it is a simple matter to cause their operation at the proper moment and before the blowing of the tension fuse or lightning arrester to cut off the current Without damaging the equipment.

The physical structure of cartridge fuses is well known and shall not be discussed in detail in this specification. However, it may be mentioned briefly, that the structure best suited for use with the present invention comprises a glass cartridge closed at both ends with metal members which are adapted to be inserted in the usual fuse holder. Inside of the cartridge may be placed one or more heat coils united by solder.

The invention is illustrated in the accompanying single sheet of drawing, showing two forms of carrying out the invention.

In one form of carrying out the invention, shown in Figs. 1 and 2, the fuse insertion comprises two heat coils 1 and 2 having resistances made of chromic nickel or constantan, and soldered together at point 3 by means of easily flowing solder, preferably such as Woods metal. The resistance loop is illustrated on a larger scale in Fig. 2, the'reference numeral 3 denoting the solder point, and the numerals 4 and 5 indicating the point where the resistance loops 1 and 2 are attachedto the springs 6 and 7. These springs in turn are attached to the fuse members 8 and 9 holding the glass cartridge 10. Arcing is in this case to a certain extent prevented by the resilience of the springs which draw apart quickly when the fuse blows. The prevention of arcing can be further improved, however, and the ohmic reslstance can be reduced, if chromic nickel wire is employed, by soldering the heat coils to copper turns. The ohmic resistance drops in this case to 0.1 0.2 ohms.

Similar relationships occur when the fuses are made of spirally wound constantan wires.

The "static load capacity is somewhat higher in-that case (about 1 1 joules), but the ohmic resistance is also higher. Referring to Figs. 3 and 4, this resistance can be considerably reduced (to about 1 ohm) by soldering or welding only a few turns, preferably only 2 turns of constantan Wire 11 on each side which are joined by Woods metal at point 12, to a spiral spring'13 made of bronze wire. The spiral spring is attached to the metal members of the cartridge. p

In order to avoid losses in all the above mentioned forms of carrying out the invention. it is irnportant to place the fuse insertion in glass cartridges, and to select these so as to correspond to the static load.

What is claimed is 1. A fuse comprising twosingle turns of nickel alloy wire soldered together by means of loW-melting-point solder, having a resistance of not more than 0.2 ohms and a static load capacity of 12 joules.

2. A cartridge fuse of low melting point with steady load and ahigh static load capacity comprising loops of chromic nickel wire soldered together with low-melting-point solder, having a resistance of not more than .2 ohms.

- In witness whereof, I hereunto subscribe my name this 2nd day of August, A. D. 1927.

' FRITZ THIERY. In witness whereof, ll hereunto subscribe my name this 2nd day of August. A. D. 1927.

' HERMANN GUETSCH. 

